1. Field of the Invention
The present invention relates to a heat-driven pump. The heat-driven pump of the present invention can be used for a pump for a room heater in a house or a building. Further, the heat-driven pump of the present invention can be used as a pump which utilizes a high temperature waste of heat discharged from a factory or a plant. Furthermore, the heat-driven pump of the present invention can be used in a remote part of the country where it is difficult to supply electric power.
2. Description of the Related Arts
Known in the art is a heat-driven pump in which the pumping action is caused by an alternate vaporization and condensation of liquid, and in which an external power device such as a motor or compressor is not required (e.g. "Heat-Driven Pump", Soda and Chlorine Magazine, 1983, No. 2, pp 64-77).
However, this heat-driven pump has an unsatisfactory performance upon starting or if an insufficient amount of heat per hour is available, which is usually caused by the use of a long copper pipe for the heating portion. This is because, in order to generate a vapor bubble from the surface of the wall of the pipe and expand the vapor bubble toward the center of the pipe, it is necessary to raise the temperature of the liquid, even the temperature of the central portion of the liquid, close to the saturation temperature of the liquid. Accordingly, a temperature of a discharged liquid is raised to an approximate saturation point and heats a pipe close to the exit of the heating portion after the pump has been in operation for sometime. In particular, when an hourly heat amount is low, the liquid temperature to the approximate saturation point cannot be quickly elevated, and therefore, because of an accompanying thermal conductivity effect from the heating portion piping, a temperature of the pipe nearest the exit of the heating portion is raised to about the liquid saturation temperature, but a vapor bubble generated at the heating portion prevents a cooling of the exit side piping. Thus, the vapor bubble is not properly condensed, and finally, the pumping action is brought to a halt. Further, a heat-driven pump of this type has a low pumping efficiency, because although a large portion of an energy is applied to the pump to heat the liquid, only a small portion of this energy can be used to create a pumping action. Further, it is required that the heat-driven pump should include two heating pipes, and the heat-driven pump should be installed on a horizontal plane.
Japanese Unexamined Patent Publication (Kokai) No. 61-31679 discloses a heat-driven pump wherein the problems described above are alleviated. Namely, in the disclosed heat-driven pump, a heating portion is shaped to facilitate the generation of vapor bubbles, and is thermally isolated from other portions of the pump. This arrangement expedites the generation of vapor bubbles, and therefore, a liquid flow rate is increased and the temperature of the discharged liquid is lowered, and thus a temperature of the outlet side piping is also lowered. Further, according to the disclosure, bubbles are easily and frequently developed and condensed, ensuring an increased flow rate and a reduced temperature, and thus a preferable cycle of functions by which the heat-driven pump achieves a smooth operation by a small or a large amount of heat is realized.
However, even in the above mentioned heat-driven pump, a vapor bubble is expanded into an outlet piping to exert a high pressure load on the external portion, and when the heat quantity of the heating is small, a bubble is expanded only slowly into the piping, thus heating the piping and preventing the bubble from being condensed. Further, since the pump provides an intake portion for bringing the expanded bubble into the condensation process by means of the capillary action, there remain problems in dealing with the needs for a heat-driven pump for a large flow rate.